To save money, time and still meet saftey standards. CVA aliens the breech plug with the barrel first, then drills and taps "through" the breech plug threads to install the nipple drum. So, in effect the nipple drum holds the breech in place. During that process, the breech threads are de-formed and if the breech plug is removed, the torn breech threads will shred the barrel threads or vice-vrs,, :cry: follow?